Long Term Evolution (LTE) is a 4G wireless broadband technology developed by the Third Generation Partnership Project (3GPP). LTE provides significantly increased peak data rates, reduced latency, scalable bandwidth capacity, and backwards compatibility with existing GSM and UMTS technology. The upper layers of LTE are based upon TCP/IP. LTE supports mixed data, voice, video and messaging traffic. LTE uses OFDM (Orthogonal Frequency Division Multiplexing) and/or MIMO (Multiple Input Multiple Output) antenna technology.
LTE radio access technology (E-UTRAN) may use enhanced inter-cell interference coordination (eICIC) functionality. The use of eICIC techniques is motivated by the emergence of denser and less coordinated network deployments with smaller cells. Having additional pico or femto co-channel layer within a typical (for example homogeneous) macro network topology can provide significant system capacity benefit. The idea is that network nodes coordinate resources between them in such a way that it enhances overall system capacity. The benefits come from the fact that user equipment (UE) may, for example, access pico layer eNBs with a better link budget compared to macro layer eNodeB (eNB), which leads to increased downlink throughput and better uplink coverage—meaning also less uplink transmit power which means less uplink interference caused to other cells.
Two basic types of example use cases have been envisioned: Macro/pico deployment and a macro/femto deployment. In a macro/pico deployment, macro nodes may mute a subset of subframes to enable terminals connected to pico nodes exchange data with reduced interference from the macro node. In a macro/femto deployment, closed-access femto nodes may mute some subframes to allow macro terminals in the vicinity of the femtos to stay connected to their serving macro cell. The muted subframes are called Almost Blank Subframes (ABS). In the muted subframes, there may still be residual interference due to transmission of Common Reference Symbols (CRS) and other physical channels containing essential information (for example system information, paging).
Time Division Multiplexing (TDM) eICIC is typically utilized when it is assumed that the user equipment may experience heavy co-channel interference from neighbor cells. In such a case, the co-channel interference patterns become time-varying by nature, partly because of TDM partitioning causing some resources to be occasionally muted. The ABS patterns utilized in TDM eICIC that are used by the network at a given point of time are unknown to the user equipment. However, subsets of the patterns, intended for restricting Radio Resource Management (RRM), Radio Link Monitoring (RLM) or Channel State Information (CSI) measurements may be configured for the UE to enable eICIC techniques. When such resource restrictions are configured, a user equipment may be signaled one subset of subframes to be used for serving cell RRM/RLM measurement purposes, one set for neighbor cell RRM measurement purposes and two subsets of subframes for CSI (CQI/PMI/RI) measurement purposes. Such subsets of subframes are also called patterns.
An Automatic Gain Control (AGC) operation in a user equipment is typically a slowly adapting loop which follows the received signal amplitude and power over several contiguous subframes in time. Its purpose is to adjust the received signal level such that the signal can be decoded properly and efficiently.
When ABS patterns are used, normal AGC operation may be degraded because received signal power fluctuates faster and with larger dynamic range than expected. In TDM eICIC operation, a user equipment receiver front-end may experience high signal amplitude in one subframe and a clearly lower signal amplitude in another subframe, which means that the variation of received power from one subframe to another depends on the ABS pattern used by network nodes (neighbor cells) and also on the overall load of the network itself. Hence, the received power variations may fluctuate heavily, leading to inefficient AGC operation.
Based on the above, there is a need for a solution that would solve or at least mitigate the above problems or drawbacks.